docs: def startswith(self, prefix, start=None, end=None):
          """Return whether the current bitstring starts with prefix.
  
          prefix -- The bitstring to search for.
          start -- The bit position to start from. Defaults to 0.
          end -- The bit position to end at. Defaults to self.len.
  
          """
          prefix = Bits(prefix)
          start, end = self._validate_slice(start, end)
          if end < start + prefix.len:
              return False
          end = start + prefix.len
          return self._slice(start, end) == prefix